Viscose process and products produced thereby



Sept 1960 R. L. MITCHELL 2,952,508

VISCOSE PROCESS' AND PRODUCTS PRODUCED THEREBY Filed Sept. 16. 1953 FIG. 2

Y INVENTOR FIG 3 Fe/d Logan N/fche/l WWW WWW ATTORNEYS 2,9525% Patented Sept. 13, 1%60 fi l-ice Reid Logan Mitchell, Shelton, onier Incorporated, Shelton, Delaware Filed Sept. 16, 1953, Set. No. 380,581 '5 Claims. (Cl. 18-54) Wash., assignor to Ray- Wash., a corporation of This invention relates to the viscose process, and has for its object the provision of improvements in the Viscose process and improved cellulosic products produced thereby. The improved products of the invention are characterized mainly by greatly increased strength and a highly ordered orientation of the crystalline elements, and by low swelling properties. While the invention is applicable generally to the coagulation and regeneration of variously shaped products which are stretched during regeneration, it is most advantageously applicable to the production of filaments for use in textiles and tire cord.

Viscose rayon filaments of general utility have many shortcomings as compared with other textile materials, manifested by low strength, particularly when wet, and high reswelling, both being attributable to a low degree of order of the regenerated structure. However, increased tensile strength in tire cord type rayon has been attained largely by prolonging the period of regeneration, permitting more time for the cellulose crystal structure to form while at the same time imposing stress to further uniaxially orient the crystalline elements being developed. Various expediencies have been resorted to to balance the conditions of coagulation and regeneration favorable to the development and orientation of crystalline elements to produce filaments having a high degree of order, high strength and low swelling properties. It has been proposed to prolong the regeneration period and keep the filaments as long as possible in a metastable, stretchable state while at the same time applying maximum stress to give a high degree of orienting stretch.

This invention provides an improved process in which the filaments receive a substantially uniform state of decomposition or regeneration throughout their cross section. The process eifects such a control over the conditions that the inner portions of the filaments are almost as accessible or responsive as the outer portions to the regenerating reagents, the entire cross section of the filaments being maintained in an intermediate state of regeneration with high stretchability for a sufiicient period to permit a relatively high degree of stretch.

In accordance with one improved process of the invention, it is important to use a viscose containing cellulose having a relatively uniform chain length at a given level within the range 300 to 800 DP. (degree of polymerization) and to spin the viscose into filaments under special chemical and physical conditions. It is advantageous in one aspect of the invention to form viscose having a salt index of from 6 to 20 and to spin the viscose into a spin bath having from 6% to 12% zinc sulfate (ZnSO or equivalent metal sulfate, preferably containing from 9% to 10% of sulfuric acid (H 80 at a temperature of from 45 to 70 C., and to stretch the filaments under controlled conditions in excess of 70%.

One embodiment of the invention comprises the incorporation of certain modifiers in the viscose spinning solution to make the filaments uniformly amenable to the action of the coagulating and regenerating reagents so that the entire cross section of the filaments, the inner portions being substantially as accessible as the outer portions, are maintained for a relatively long period in an intermediate state of regeneration during which time the filaments are susceptible to high stretchability. Modifiers effective in the process of the invention for incorporation in the viscose include non-ionic agents, such as the block copolymers of polyethylene oxide and polypropylene oxide, for example those known as Pluronics. The block copolymers sold under the name Pluronics are produced by the Wyandotte Chemical Corporation. Particular block copolymers known as Pluronics L-62, L-64, L-61, L-44, and F-68 give eflfective results, L64 being particularly effective. Among other agents which show some regeneration retarding action are the simple polyethylene oxides, polypropylene oxides and compounds of alkylphenolethylene oxide condensation products. These agents may be added to the viscose alone or in combination, or in combination with amines, for example cyclohexylamine. These non-ionic agents are carried along into the spin bath where they accumulate and, among other things, suppress the formation of craters on the spinnerets. It has been common practice to use such anticratering agents in spin baths to prevent crater formation but around 0.005% by weight based on the viscose has been suificient for this purpose. In this process, the surprising results in the control of regeneration require, say, from 0.1% to 1.0% by weight based on the viscose added in the viscose itself. With regard to the block copolymers, there is a sufiicient carryover to the spin bath to build up a substantial equilibrium value which modifies the reaction in which the cellulose xanthate is decomposed to yield cellulose. The block copolymers in particular, when used in the amounts of the invention, are in some instances thrown out of solution and form a floating layer on the surface of the spin bath. It may be that there is a sufiicient amount of the block copolymer in viscose and the spin bath to coat the freshly extruded filaments and efiect a retardation of the penetration of the acid while permitting entry of the zinc, thereby permitting more extensive stretch. It is preferred to allow the spin bath to reach equilibrium conditions before attempting to spin high tenacity filaments.

While the resulting action is not fully understood at this time, it appears that these non-ionic agents not only remove resin particles from the surface but also from the interior of the filaments. They make it possible in conjunction with high concentrations of zinc sulfate or equivalent metal sulfate in the spin bath to maintain with good continuity extremely high orienting stretch. The spinning conditions of the invention result in a relatively long period of regeneration during which time the filaments are stretched so as to achieve a high degree of order, high strength and low swelling properties. In order to effect a proper control over the decomposition and regeneration of the filaments, it is preferred to provide a long bath travel before gathering the filaments, for example, a distance of around 15 to 30 inches or more, depending on spinning speed, from the spinneret to the gathering hook. A total bath travel of around to 250 inches generally gives satisfactory results. Suitable arrangements may be made to change the stretch pattern, eifect earlier stretch and increased tension by the use of large tension wheels. Suitable long contact with the spin bath while undergoing high stretch may be accomplished by use of a modified stretching setup on the Kuljian machine or other pot, bobbin or continuous type spinning frame.

The viscose may be modified further by adding directly to the viscose suitable inorganic or organic zinc compounds to aid in controlling the uniformity of regeneration. It appears that the process of the invention causes a more effective and complete penetration of the zinc of the spin bath into the center of the filaments. This action may be further aided by the incorporation of suitable zinc compounds into the viscose before spinning.

In another aspect of the invention, -1 incorporate certain agents in the spin bath to control the regeneration of the filaments. In a preferred embodiment of this aspect of the invention, dimethyl formarnide is added to and dissolved in the spin bath. While the full effect of this compound is not at this time known, it appears that it has a greening or regeneration retarding action on the filaments and may also function as a gas solvent to suppress the formation of gas as such within the green filaments. The action appears to facilitate uniform retarded entry of regenerating agents and the consolidation of the filaments. It is possible that the prevention of gas bubbles within the green filaments prevents the formation of areas of weakness that would otherwise persist through regeneration in a high zinc bath without added retardants.

Still other aspects of spin bath treatment may comprise the incorporation in the spin bath of other amides the combination of Pluronics and amines, and the combination of Pluronics, amines and dimethyl formamide.

In one of its more complete embodiments, the invention comprises incorporating one or more of the agents, such as Pluronics or other retardants having like greening properties in the viscose, with or without added zinc bearing compounds and amines, and the spinning of the viscose thus treated into a spin bath to which has been added dimethylformamide with or without added other amides, and preferably co'ntaining a relatively high content of zinc such as Zinc sulfate or equivalent metal sulfate, such as iron or manganese.

In accordance with a process of the invention, the filaments are preferably given a relatively long travel through the spin bath adjusted to spinning speed and during regeneration the filaments are subjected to an exceptional amount of stretch, varying, say, from 70% to around 200%, and even up to 1000%. The resulting filaments, when given the common differential dye test to distinguish skin from core, appear to be all-skin, and have tensile strengths upwards of 3.5 g. per denier while exhibiting exceptional resistance to fatigue.

In carrying out the process of the invention, a viscose may be spun having a D.P. level of from 300 to 800 and relatively uniform chain length prepared from celluloses such as sulfite wood cellulose, for example, Rayocord X, prehydrolyzed kraft, cotton linters, resin free pulp, high D.P. pulp of uniform chain length, and preodixized pulp of low D.P. and uniform chain length.

The viscose solution may comprise cellulose and caustic soda in any suitable proportions, the cellulose varying from 7% to 13% and the caustic soda varying from 6.0% to 13%. Particular viscose solutions may comprise:

and 6.5% and 7.0% and 8.0% and 12.0% and 9.0% and 13.0%

caustic soda caustic soda caustic soda caustic soda caustic soda caustic soda cellulose cellulose cellulose cellulose cellulose cellulose 4 xanthation. Also, low mixing temperatures, such as 12 C. may be advantageously used to maintain sodium chloride index.

In carrying out a more or less complete operation in one embodiment of the invention, a block copolymer of polyethylene oxide and polypropylene oxide represented by the formula in which x has an average value of about 16 and y has an average value of about 28 is mixed into the viscose spinning solution in amounts varying from 0.1% to 1.0% by weight based on the viscose. The compound Pluronic L64 is of this type and is very etfective for carrying out this aspect of the invention. It appears that the use of a block copolymer in the viscose, in addition to the dispersion of resins as aforementioned, also retards regeneration and alleviates the formation of gas bubbles in the green viscose during decomposition. Regardless of the action of the block copolymer, its use facilitates the use of relatively high concentrations of Zinc sulfate in the spin bath and results in cumulatively retarding the rate of regeneration whereby the filaments may be stretched more extensively during their transformation from the green state to a highly oriented crystalline structure. The action of the block copolymer may be further accentuated by adding dimethylformamide (DMF) to the spin bath in amounts of about 0.2% or more. The DMF acts as a greening agent and appears also to act as a gas solvent or in some manner to control the conditions which inhibit the formation of gas bubbles in the filaments. When the DMF is used in a spin bath for the spinning of viscose containing a block copolymer, the production of all-skin filaments, of superior rounded cross-sectional shape, free of bubbles, of high tensile strength and improved fatigue properties is facilitated.

The term all-skin comes from a dyeing technique now in common use whereby thin filament cross sections are processed with certain dyes which act selectively with respect to ordered and disordered cellulose. Ordinary textile rayon cross-dyed by this method shows a thin outer skin of highly ordered cellulose dyed in one color surrounding a low-ordered core of much larger area dyed in another color. Regular tire cord rayon dyed in the same manner shows a much thicker skin of high order surrounding a smaller core of low order.

In the accompanying drawings, the cross sections of the filaments are under a magnification of 2200 and were dyed as described, the dark portions representing the highly ordered and oriented skin portions.

Fig. 1 illustrates the cross sections of ordinary textile rayon filaments;

Fig. 2 illustrates ordinary tire cord rayon filaments, and

Fig. 3 illustrates all-skin rayon filaments of the invention.

The following examples illustrate processes carried out according to the invention:

Example 1 A viscose of 7.5% cellulose content, 6.5% sodium hydroxide and 0.5% of added Pluronic L64 was spun at a sodium chloride index of 15.0 into a spin bath of 9.5% H 20% Na SO 9% ZnSO and 1.0% added (DMF) dimethylformamide maintained at 58 C. The extruded filaments corresponding to 1650/ 720 yarn were led around a system of vaned rollers for a distance of 200 inches, stretched 250% in the bath, withdrawn from the bath onto a godet under a tension of 1200 grams, treated with hot water at 80 C., stretched an additional 50% under a tension of 1600 grams and wound on a bobbin at 50 meters/minute. The primary stretch of 250% is determined from the relative speed of the collected filaments as they pass about the first vaned roller as related to the speed on exit from the spin bath; secondary stretch is the additional stretch given in the hot water prior to windup; total stretch relates the speed at windup to speed at initial roller (e.g., first measurable reference point).

Filaments of this yarn were substantially all-skin and cord made therefrom in 2 ply 12/ twist at 3650 denier had a conditioned (60% RH, 75 F.) tenacity of 3.5 g./denier with elongation of 13.2%, wet tenacity of 2.5 g./denier, fatigue life of 450 and reswelling value in water of 170. Normal medium-skin tire cord of similar construction spun from similar viscose without L-64 at normal index 5.5 and into a 9.5-23-3.5 spin bath without added DMF had a conditioned tenacity of 2.8 g./denier with elongation of 12.5%, wet tenacity of 1.8, fatigue life of 300 and reswelling value of 205.

Example 2 A viscose of 7.5% cellulose content and 6.5% sodium hydroxide was spun at 15.0 sodium chloride index into a spin bath of 9.0% H 80 18% Na SO 9% ZnSO 0.1% (LPC) lauryl pyridinium chloride and 1.0% DMF at 48 C. The extruded filaments (720 to yield total finished denier of 1650) were led through a system of vaned rollers for a bath travel of 250 inches, stretched 210% in the bath, withdrawn onto a godet under a tension of 1300 grams, treated with hot water at 80 (3., stretched an additional 50% under a tension of 1800 grams and wound on a bobbin at 80 meters/minute.

Filaments of this yarn were 90+% skin and cord made therefrom in 2 ply 12 x 10 construction of 3650 denier had a conditioned tenacity of 3.45 g./denier with fatigue life of 419.

Example 3 A viscose of 7.5% cellulose content, 6.5% sodium hydroxide and 0.2% added L-64 at a viscosity of 35 seconds ball fall (50 poises, 400 DP.) and index of 4.5 was spun into a bath of 9.5% H 80 23% Na SO 9.0% ZnSO; and 1.0% DMF at 52 C. The extruded filaments (100 to yield total finished denier of 300) were led through a system of vaned rollers for a bath travel of 250 inches, stretched 200% in the bath, withdrawn onto a godet under a tension of 280 grams, treated with hot water at 80 C., stretched an additional 50% under a tension of 300 grams and wound on a bobbin at 100 meters/minute.

Filaments of this yarn were substantially all-skin and when given 2 turns/inch twist had a conditioned tenacity of greater than 4 grams/denier with elongation of a wet tenacity of greater than 2.5 grams/denier and reswelling value of 170 as compared with regular textile yarn values of 2.0, 1.0 and 230.

Example 4 Assume a viscose of 7.5% cellulose and 6.5 sodium hydroxide being spun at 15 index into a bath of 9.5 H SO Na SO 9.0% ZnSO and 0.1% LPC at 48 C. The extruded filaments are led through a system of vaned rollers for a bath travel of 200 inches, stretched 50% in the bath, Withdrawn onto a godet under a tension of 1400 grams, treated with hot water at 80 C., stretched an additional 20% under a tension of 1800 grams and wound on a bobbin at 50 meters/minute.

Filaments of this yarn are rather brittle and break frequently under the applied tension causing roller wraps and interruptions in spinning. The resultant finished yarn is rather cheesy, contains voids resulting from entrapped gas, has thin skin and a conditioned strength of only 2.8 grams/denier and fatigue life in the range 100-300 when twisted into a 3650 denier cord of 2 ply 12/ 10 construction.

When 1.0% DMF is added to the spin bath, the yarn becomes greener, tensions go down, and the stretch increases. Larger vaned rollers may then be added to bring tensions up and further increase the stretch to a value of about 200% in the bath and 50% in the hot water. The resultant cord has a conditioned strength above 3.3 grams/denier and fatigue life in the range 400-600.

When 0.5% L-64 is used in the viscose along with DMF in the spin bath, the yarn becomes still more green, tensions go down still further and stretch may be correspondingly increased to values of around 300% in bath and 70% in hot water yielding a resultant cord of above 3.5 grams/denier conditioned strength and fatigue life in the range 500-700.

Example 5 A filtered deaerated viscose of 7.5 cellulose content and 6.5% sodium hydroxide content having a sodium chloride index of 15.0 and containing an added 0.5% on Weight of the viscose of a reaction buffering Zinc carrier, in this case Pluronic L-64, Was extruded into a spin bath maintained at 60 C. and containing 9.0% H SC 18.0% N21 SO 9.0% ZnSO and an added 1.0% gas solvent, in this case DMF. The thread of collected filaments was led through the bath and around tension wheels building up a tension of about 0.8 gram/denier while being stretched about over a path of 20 inches. The thread was withdrawn from the bath by a godet on which Was dripped hot water at C., then transferred to a second godet with 25% added stretch at a tension of about 0.9 gram per denier and wound-up on a bobbin at meters per minute after a total stretch of about 100%. The und ried thread, Washed acid free, was slashed in an oil emulsion bath with no additional stretch, dried on the slasher and led directly over tensioning devices (0.3 gram/denier) to a ring twister to form 1650 denier singles which were then cabled in 12 x 10 construction to give a cord having 3650 total denier and 1440 total filaments.

The cord tested at 75 F. and 60% RH. had a tenacity of 3.6 g./d. and elongation at break of 13.2% with a fatigue test of 455 and reswelling value of 180. Cornparable figures for standard tire cord are respectively 2.8, 12.0, 300 and 205. The dyed filament cross section shown in Fig. 3 is typical of the cord in the example and that in Fig. 2 of standard cord.

Example 6 A viscose of 7.5% cellulose and 6.5% sodium hydroxide content at 16.5 NaCl index was extruded through a 100 hole spinneret at a rate to give a finished thread of 275 denier into a spin bath having 9% H SO 17% Na SO 9.5% ZnSO and 1.0% added DMF maintained at 48 C. The filaments were passed around an initial large vaned roller followed by subsequent smaller rollers to build up an early stretch pattern and wound up at a speed of 50 meters/minute following a total stretch of 950% with primary tension of 250 grams and secondary tension of 300 grams.

The all-skin yarn was given a twist of 2 t.p.i., desulfured, bleached and dried. The finished yarn of 275 denier had a conditioned tenacity of 4.3 grams/denier, wet tenacity of 3.0, B.D. tenacity of 5.0, elongation at break of 15.8%, gel swelling of 170.

Example 7 A viscose of 7.5% cellulose and 6.5% sodium hydroxide content at 17.8 NaCl index was extruded through a 720 hole spinneret at a rate to give a thread of 1650 final denier into a spin bath having 9.5% H SO 18% Na SO 9.0% ZnSO and 1.0% added DMF maintained at 49 C. After a travel in the bath of 26" the filaments were collected by a hook guide, passed around vaned rollers submerged in the bath for an additional 100" While being stretched 300% and brought to a tension of 1100 grams at exit from the bath, the stretch pattern showing a high degree of early stretch. On exit from the spin bath the yarn was passed around a godet, washed with 80 C. water, stretched an additional 50% at a tensionof 1500 grams, relaxed and wound up on a bobbin at SO'meters/minute.

A 2 ply 11 x 11 twist cord prepared from this yarn had a conditioned (60% R.H., 75 F.) tenacity of 3.5 grams/ denier, a wet tenacity of 2.5 grams/ denier, a B.D. tenacity of 4.2 grams/denier, an elongation at break of 13.8%, and a fatigue life of 545.

Example 8 To illustrate the retarding action of the various regeneration retardants, a viscose of 7.5% cellulose and 6.5% sodium hydroxide was prepared at 15.0 salt index. Congo red was added to the extent of about 0.1% based on the viscose. The viscose was then divided into several portions. One portion was labeled as the control and held without further additions. To successive other portions 0.5% of Pluronic L-64, Pluronic F-58 and cyclohexylamine were added. The four viscose samples were east side by side as films (10 mils thick) on a glass plate which was then immersed into a spin bath of 9.5% H 80 18% Na SO 9.0% ZnSO and 1.0% of added DMF maintained at 48 C. The time required for a change in color of the red viscose to blue film was as follows: About 50 seconds for the control, 120 seconds for viscose containing L-64, 120 seconds for viscose containing cyclohexylamine, 300 seconds for viscose containing F68.

Under similar conditions with DMF omitted from the bath the time required for change in color was about 45 seconds for the control, 100 seconds for L-64, 100 seconds for cyclohexylamine and 200 seconds for F-68.

Under similar conditions with both the ZnSO and DMF entirely omitted from the bath, the color change time Was about 40 seconds for all samples.

I claim:

1. In the viscose process the improvement which comprises providing a viscose spinning solution having a salt index of from 6 to 20 and formed of cellulose having from 300 to 800 degrees of polymerization, incorporating in the viscose from 0.1% to 1% of a block copolymer of polyethylene oxide and polypropylene oxide, spinning the viscose into a spin bath containing from 6% to 12% of zinc sulfate at a temperature of from 45 to 70 C. and to which dimethyl formamide was added, passing the filaments in contact with spin bath solution for a distance of at least 150 inches, and during regener- 0 ation stretching the filaments at least thereby pro-. ducing high strength all-skin filaments.

2. In the viscose process the improvement which comprises providing a viscose spinning solution containing cellulose having a degree of polymerization of from 300 to 800, incorporating in the viscose from 0.1% to 1.0% of a block copolymer of polyethylene oxide and polypropylene oxide as a regeneration retardant, and spinning the viscose into a spin bath containing from 6% to 12% of a zinc salt to which was added at least 0.2% of 'dimethylformamide, and stretching the resulting filaments during regeneration thereby producing all-skin filaments;

3. In the process of claim 2, adding to the viscose a block copolymer represented by the formula HO(CH2CH2O)x(CHOH2O) (OH2CH2O) E (3113 in which x has an average value of about 16 and y has an average value of about 28.

4. In the process of claim 2, passing the extruded filaments through at least 20 inches of spin bath and stretching the filaments during regeneration at least 70% producing all-skin filaments.

5. In the process of claim 1, using a block copolymer represented by the formula Ho 011201120).(oHoHZmflOmOEw)XE CH3 in which x has an average value of about 16 and y has an average value of about 28.

References Cited in the file of this patent UNITED STATES PATENTS Re. 24,486 lVIitchell June 10, 1958 2,225,604 Lubs Dec. 17, 1940 2,297,746 Charch Oct. 6, 1942 2,362,217 Schlosser et al. Nov. 7, 1944 2,393,817 Schlosser et al. Jan. 29, 1946 2,535,044 Cox Dec. 26, 1950 2,535,045 Cox Dec. 26, 1950 2,586,796 Drisch et al. Feb. 26, 1952 2,592,355 Tachikawa Apr. 8, 1952 2,607,955 Drisch et al Aug. 26, 1952 2,620,258 McLellan Dec. 2, 1952 2,731,667 Bradshaw Jan. 24, 1956 2,805,169 Mitchell Sept. 3, 1957 

1. IN THE VISCOSE PROCESS THE IMPROVEMENT WHICH COMPRISES PROVIDING A VISCOSE SPINNING SOLUTION HAVING A SALT INDEX OF FROM 6 TO 20 AND FORMED OF CELLULOSE HAVING FROM 300 TO 800 DEGREES OF POLYMERIZATION, INCORPORATING IN THE VISCOSE FROM 0.1% TO 1% OF A BLOCK COPOLYMER OF POLYETHYLENE OXIDE AND POLYPROPYLENE OXIDE, SPINNING THE VISCOSE INTO A SPIN BATH CONTAINING FROM 6% TO 12% OF ZINC SULFATE AT A TEMPERATURE OF FROM 45* TO 70*F. AND TO WHICH DIMETHYL FORMAMIDE WAS ADDED, PASSING THE FILAMENTS IN CONTACT WITH SPIN BATH SOLUTION FOR A DISTANCE OF AT LEAST 150 INCHES, AND DURING REGENERATION STRETCHING THE FILAMENTS AT LEAST 70% THEREBY PRODUCING HIGH STRENGTH ALL-SKIN FILAMENTS. 